Turbines are widely used in industrial and commercial operations. A typical commercial steam or gas turbine used to generate electrical power includes alternating stages of stationary and rotating airfoils. For example, stationary vanes may be attached to a stationary component such as a casing that surrounds the turbine, and rotating blades may be attached to a rotor located along an axial centerline of the turbine. A compressed working fluid, such as but not limited to steam, combustion gases, or air, flows through the turbine, and the stationary vanes accelerate and direct the compressed working fluid onto the subsequent stage of rotating blades to impart motion to the rotating blades, thus turning the rotor and performing work.
The efficiency of the turbine generally increases with increased temperatures of the compressed working fluid. However, excessive temperatures within the turbine may reduce the longevity of the airfoils in the turbine and thus increase repairs, maintenance, and outages associated with the turbine. As a result, various designs and methods have been developed to provide cooling to the airfoils. For example, a cooling media may be supplied to a cavity inside the airfoil to convectively and/or conductively remove heat from the airfoil. In particular embodiments, the cooling media may flow out of the cavity through cooling passages in the airfoil to provide film cooling over the outer surface of the airfoil.
As temperatures and/or performance standards continue to increase, the materials used for the airfoil become increasingly thin, making reliable manufacture of the airfoil increasingly difficult. Specifically, the airfoil is typically cast from a high alloy metal, and a thermal barrier coating may be applied to the outer surface of the airfoil to enhance thermal protection. The cooling passages are often drilled or machined into the high alloy metal at precise locations and in precise geometries after casting to optimize the cooling media flow over the airfoil. For example, a water jet may be used to drill the cooling passages through the high alloy metal at particular locations and angles to enhance the cooling media flow over the outer surface of the airfoil. Although effective at accurately drilling small diameter holes through the high metal alloy, the water jet may also damage the thermal barrier coating and/or introduce grit byproducts inside the airfoil that may be difficult to completely remove. Alternately or in addition, the water jet may inadvertently strike the interior of the airfoil on the opposite side of the cavity causing damage inside the airfoil. The grit byproducts inside the airfoil and/or damage to the interior of the airfoil may be difficult to detect during the finishing steps of the airfoil. As a result, a system and method for manufacturing an airfoil that reduces or prevents the damage to the thermal barrier coating, introduction of grit byproducts into the airfoil, and/or inadvertent damages to the interior of the airfoil would be useful.